# BJT questions

Discussion in 'Homework Help' started by KillerZ123, Feb 5, 2011.

1. ### KillerZ123 Thread Starter New Member

Nov 25, 2010
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0

I have this circuit and I am trying to determine Ic and VCE and operation mode. I am not sure if I am doing this correctly. Here is what I did:

I am given beta = 100 and VBE = 0.715v

I said the nod at the emitters is -0.715v therefore the emitter current is:

$I_{E} = \frac{-0.715v - (-15v)}{180x10^{3}\Omega} = \frac{79x10^{-6}A}{2} = 39.7\mu A$

The collector current is:

$I_{c} = I_{E}\alpha = (39.7x10^{-6})(0.99) = 39.3\mu A$

$V_{CE} = V_{CC} - I_{C}R_{C} + V_{E} = 5v - (49.9x10^{3}\Omega)(39.3x10^{-6}\mu A) + (-0.715v) = 2.32v$

The transistors are in forward-active mode.

Dec 26, 2010
2,147
300
Check your signs carefully. Vce = Vc - Ve, not Vc + Ve

3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
Just to make the point - everything other than Vce looks fine.

4. ### KillerZ123 Thread Starter New Member

Nov 25, 2010
7
0
Thanks. I am not sure why I put the + instead of the -.